Network taps are devices used to monitor traffic in live networks. A network tap receives a signal from the network, copies or diverts the signal to one or more monitoring processors, and transmits the original signal back to the network. In today's high speed networks, network taps tap optical and electrical signals.
Because a network tap is typically used as inline component, the network operator needs to account for the case when the network tap fails, for example, due to loss of external power. Network taps include pairs of ports that connect to the network. One port of a port pair may connect to a cable to receive a signal from the network, and another port of the pair may connect to a cable to provide the signal back to the network. If a failure of external power occurs, one type of network tap automatically fails open to allow traffic to pass through the network tap. Traffic flow continuity is provided by optical switches connected between ingress and egress port pairs that close when external power is disconnected. The optical switches do not require power to close and thus prevents an interruption in traffic flow to or from the network.
One problem with utilizing optical switches between network tap ports to provide automatic fail open capability is that an optical switch must be provided for each ingress/egress port pair in the network tap, and optical switches are expensive. For a network tap that includes multiple port pairs, providing an optical switch between every port pair can greatly increase the cost of the network tap.
Another feature of some network taps when external power is disconnected is temporary battery backup of all of the components of the network tap, including the components that perform network monitoring functions. For these taps, when external power fails, a backup battery allows the tap to function in the same mode as the tap functioned prior to the failure. That is, the battery powers the full network monitoring functionality of the network tap. One problem with such an approach is that a large battery may be required to fully power the tap for extended periods of time when external power is lost.
Another problem with existing network taps is that the taps either fail open or fail closed. “Fail open”, as used herein, means that the network tap allows network traffic between ingress and egress network port pairs. “Fail closed” means that the network tap blocks network traffic between ingress and egress port pairs. Such inflexibility in failover operation limits the utility of such network taps.